In vivo electrophysiological evidence for tonic activation by endogenous noradrenaline of alpha 2-adrenoceptors on 5-hydroxytryptamine terminals in the rat hippocampus

Noradrenergic alterations in Parkinson's disease: a combined 11C-yohimbine PET/neuromelanin MRI study

Degeneration of the noradrenergic system is now considered a pathological hallmark of Parkinson's disease, but little is known about its consequences in terms of parkinsonian manifestations. Here, we evaluated two aspects of the noradrenergic system using multimodal in vivo imaging in patients with Parkinson's disease and healthy controls: the pigmented cell bodies of the locus coeruleus with neuromelanin sensitive MRI; and the density of α2-adrenergic receptors (ARs) with PET using 11C-yohimbine. Thirty patients with Parkinson's disease and 30 age- and sex-matched healthy control subjects were included. The characteristics of the patients' symptoms were assessed using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). Patients showed reduced neuromelanin signal intensity in the locus coeruleus compared with controls and diminished 11C-yohimbine binding in widespread cortical regions, including the motor cortex, as well as in the insula, thalamus and putamen. Clinically, locus coeruleus neuronal loss was correlated with motor (bradykinesia, motor fluctuations, tremor) and non-motor (fatigue, apathy, constipation) symptoms. A reduction of α2-AR availability in the thalamus was associated with tremor, while a reduction in the putamen, the insula and the superior temporal gyrus was associated with anxiety. These results highlight a multifaceted alteration of the noradrenergic system in Parkinson's disease since locus coeruleus and α2-AR degeneration were found to be partly uncoupled. These findings raise important issues about noradrenergic dysfunction that may encourage the search for new drugs targeting this system, including α2-ARs, for the treatment of Parkinson's disease.

[Antidepressants - stimulators for the release of norepinephrine and serotonin (history of creation, study of neurochemical effects and classification)]

The history of the creation and putting into practice of antidepressants and experimental agents - blockers of α₂-adrenergic receptors and serotonin 5-HT₂-receptors is described. The author analyzes the history of development of mianserin, mirtazapine and other drugs and their position in the classification of antidepressants. On the basis of a generalization of historical facts, the rationality of assigning mianserin, mirtazapine, and possibly other compounds similar in chemical structure and mechanism of action to one neurochemical group and its designation by the term 'stimulators of the release of norepinephrine and (presumably) serotonin' is determined.

Role of central serotonin and noradrenaline interactions in the antidepressants' action: Electrophysiological and neurochemical evidence

The development of antidepressant drugs, in the last 6 decades, has been associated with theories based on a deficiency of serotonin (5-HT) and/or noradrenaline (NA) systems. Although the pathophysiology of major depression (MD) is not fully understood, numerous investigations have suggested that treatments with various classes of antidepressant drugs may lead to an enhanced 5-HT and/or adapted NA neurotransmissions. In this review, particular morpho-physiological aspects of these systems are first considered. Second, principal features of central 5-HT/NA interactions are examined. In this regard, the effects of the acute and sustained antidepressant administrations on these systems are discussed. Finally, future directions including novel therapeutic strategies are proposed.

Effect of combined treatment with aripiprazole and antidepressants on the MK-801-induced deficits in recognition memory in novel recognition test and on the release of monoamines in the rat frontal cortex

According to preclinical and clinical studies, the antidepressant-induced increase in the activity of atypical antipsychotics may efficiently improve the treatment of negative and some cognitive symptoms of schizophrenia. In the present study, we aimed to evaluate the effects of the antidepressants escitalopram and mirtazapine and the atypical antipsychotic drug aripiprazole, administered separately or in combination, on the MK-801-induced deficits in the recognition memory test and on the extracellular levels of monoamines and their metabolites in the rat frontal cortex. Based on the results of the behavioral tests, co-treatment with an ineffective dose of aripiprazole (0.1 mg/kg) and escitalopram (2.5 and 5 mg/kg) or mirtazapine (5 mg/kg) abolished the deficits evoked by MK-801 in the novel object recognition test, and those effects were blocked by the 5-HT_1A receptor antagonist (WAY 100,635) or the dopamine D₁ receptor antagonist (SCH 23,390). Moreover, co-treatment with aripiprazole (0.3 mg/kg) and escitalopram (5 mg/kg) significantly increased the levels of noradrenaline and serotonin, decreased the level of its metabolite, and did not alter level of dopamine, but decreased the levels of its metabolites. In addition, co-treatment with aripiprazole (0.3 mg/kg) and mirtazapine (10 mg/kg) significantly increased the level of noradrenaline, did not change the levels of dopamine and serotonin, but increased the levels of their metabolites. Based on these results, the increase in the extracellular levels of noradrenaline or serotonin in the cortex induced by co-treatment with an antidepressant and aripiprazole may be very important for the pharmacotherapy of negative and some cognitive symptoms of schizophrenia.

In vivo electrophysiological recordings of the effects of antidepressant drugs

Antidepressant drugs are a standard biological treatment for various neuropsychiatric disorders, yet relatively little is known about their electrophysiologic and synaptic effects on mood systems that set moment-to-moment emotional tone. In vivo electrical recording of local field potentials (LFPs) and single neuron spiking has been crucial for elucidating important details of neural processing and control in many other systems, and yet electrical approaches have not been broadly applied to the actions of antidepressants on mood-related circuits. Here we review the literature encompassing electrophysiologic effects of antidepressants in animals, including studies that examine older drugs, and extending to more recently synthesized novel compounds, as well as rapidly acting antidepressants. The existing studies on neuromodulator-based drugs have focused on recording in the brainstem nuclei, with much less known about their effects on prefrontal or sensory cortex. Studies on neuromodulatory drugs have moreover focused on single unit firing patterns with less emphasis on LFPs, whereas the rapidly acting antidepressant literature shows the opposite trend. In a synthesis of this information, we hypothesize that all classes of antidepressants could have common final effects on limbic circuitry. Whereas NMDA receptor blockade may induce a high powered gamma oscillatory state via direct and fast alteration of glutamatergic systems in mood-related circuits, neuromodulatory antidepressants may induce similar effects over slower timescales, corresponding with the timecourse of response in patients, while resetting synaptic excitatory versus inhibitory signaling to a normal level. Thus, gamma signaling may provide a biomarker (or “neural readout”) of the therapeutic effects of all classes of antidepressants.

Anti-stress neuropharmacological mechanisms and targets for addiction treatment: A translational framework

Stress-related substance use is a major challenge for treating substance use disorders. This selective review focuses on emerging pharmacotherapies with potential for reducing stress-potentiated seeking and consumption of nicotine, alcohol, marijuana, cocaine, and opioids (i.e., key phenotypes for the most commonly abused substances). I evaluate neuropharmacological mechanisms in experimental models of drug-maintenance and relapse, which translate more readily to individuals presenting for treatment (who have initiated and progressed). An affective/motivational systems model (three dimensions: valence, arousal, control) is mapped onto a systems biology of addiction approach for addressing this problem. Based on quality of evidence to date, promising first-tier neurochemical receptor targets include: noradrenergic (α1 and β antagonist, α2 agonist), kappa-opioid antagonist, nociceptin antagonist, orexin-1 antagonist, and endocannabinoid modulation (e.g., cannabidiol, FAAH inhibition); second-tier candidates may include corticotropin releasing factor-1 antagonists, serotonergic agents (e.g., 5-HT reuptake inhibitors, 5-HT3 antagonists), glutamatergic agents (e.g., mGluR2/3 agonist/positive allosteric modulator, mGluR5 antagonist/negative allosteric modulator), GABA-promoters (e.g., pregabalin, tiagabine), vasopressin 1b antagonist, NK-1 antagonist, and PPAR-γ agonist (e.g., pioglitazone). To address affective/motivational mechanisms of stress-related substance use, it may be advisable to combine agents with actions at complementary targets for greater efficacy but systematic studies are lacking except for interactions with the noradrenergic system. I note clinically-relevant factors that could mediate/moderate the efficacy of anti-stress therapeutics and identify research gaps that should be pursued. Finally, progress in developing anti-stress medications will depend on use of reliable CNS biomarkers to validate exposure-response relationships.

Brexpiprazole: so far so good

This article describes the role of a newly approved antipsychotic agent brexpiprazole in the treatment of schizophrenia and major depressive disorder. This drug has high affinity for 5-HT1A, 5-HT2A, D2 and α1B,2C receptors. It displays partial agonism at 5-HT1A and D2 receptors and potent antagonism at 5-HT2A and α1B,2C adrenergic receptors. It also has some affinity (antagonism) for D3, 5-HT2B, 5-HT7 and α1A,1D receptors, and moderate affinity for H1 and low affinity for M1 receptors. These all lead to a favorable antipsychotic profile in terms of improvement of cognitive performance and sleep patterns, as well as effects on affective states and potential to treat core symptoms in schizophrenia and major depressive disorder, including cognitive deficits with a low risk of adverse effects (extrapyramidal symptoms, metabolic complications, weight gain, akathisia potential) that are commonly encountered with other typical and second-generation antipsychotic drugs. In our review, we have made an attempt to decipher the pharmacological profile of brexpiprazole from two major trials (VECTOR and BEACON). We have also tried to give a concise but detailed overview of brexpiprazole by head to head comparison of the pharmacological profile of brexpiprazole and its earlier congeners aripiprazole and prototype antipsychotic drug chlorpromazine by accessing individual summaries of product characteristics from the US Food and Drug Administration database, 2015. Relevant preclinical and clinical studies associated with this drug have been discussed with emphasis on efficacy and safety concerns. From the studies done so far, it can be concluded that brexpiprazole can be an effective monotherapy for schizophrenia and as an adjunct to other antidepressant medications in major depressive disorder.

Brexpiprazole Alters Monoaminergic Systems following Repeated Administration: an in Vivo Electrophysiological Study

BACKGROUND

Brexpiprazole was recently approved as adjunctive therapy for depression and treatment of schizophrenia in adults. To complement results from a previous study in which its acute effects were characterized, the present study assessed the effect of repeated brexpiprazole administration on monoaminergic systems.

METHODS

Brexpiprazole (1mg/kg, subcutaneous) or vehicle was administered once daily for 2 and 14 days. Single-unit electrophysiological recordings from noradrenaline neurons in the locus coeruleus, serotonin neurons in the dorsal raphe nucleus, dopaminergic neurons in the ventral tegmental area, and pyramidal neurons in the hippocampus CA3 region were obtained in adult male Sprague-Dawley rats under chloral hydrate anesthesia within 4 hours after final dosing.

RESULTS

Brexpiprazole blunted D2 autoreceptor responsiveness, while firing activity of ventral tegmental area dopaminergic neurons remained unaltered. Brexpiprazole increased the firing rate of locus coeruleus noradrenaline neurons and increased noradrenaline tone on α2-adrenergic receptors in the hippocampus. Administration of brexpiprazole for 2 but not 14 days increased the firing rate of serotonin neurons in the dorsal raphe nucleus. In the hippocampus, serotonin1A receptor blockade significantly disinhibited pyramidal neurons after 2- and 14-day brexpiprazole administration. In contrast, no significant disinhibition occurred after 24-hour washout or acute brexpiprazole.

CONCLUSIONS

Repeated brexpiprazole administration resulted in a marked occupancy of D2 autoreceptors, while discharge activity of ventral tegmental area dopaminergic neurons remained unaltered. Brexpiprazole enhanced serotonergic and noradrenergic tone in the hippocampus, effects common to antidepressant agents. Together, these results provide further insight in the neural mechanisms by which brexpiprazole exerts antidepressant and antipsychotic effects.

Investigation of allyphenyline efficacy in the treatment of alcohol withdrawal symptoms

We have recently demonstrated that allyphenyline, behaving as α2C-adrenoceptor/serotonin 5-HT1A receptor agonist and α2A-adrenoceptor antagonist, in mice enhanced morphine analgesia, attenuated morphine withdrawal symptoms, showed significant antidepressant-like activity and was devoid of sedative side effects. Opioid and alcohol withdrawal shares several common neurobiological and molecular mechanisms. Therefore, in this study we expanded our analysis of the pharmacological properties of allyphenyline by investigating its ability to prevent the expression of somatic withdrawal signs, anxiety-like behavior and hyperlocomotion associated with chronic ethanol intoxication. Rats were subjected to induction of ethanol dependence via repeated daily intragastric ethanol (20%) administration for 4 consecutive days. Twelve hours after the last alcohol administration, somatic alcohol withdrawal signs were scored. Results revealed a significant expression of physical withdrawal signs that were not affected by intraperitoneal (i.p.) administration of allyphenyline at the doses of 0.05, 0.275 and 0.5 mg/kg. In contrast, allyphenyline (0.05 and 0.275 mg/kg i.p.) significantly reduced hyperanxiety-like behavior observed 6 days after alcohol intoxication as measured using the defensive burying test. Allyphenyline also reduced open field hyperlocomotor activity associated with alcohol withdrawal. Notably, the anxiolytic effect of the compound, as well as the already reported antidepressant action, was observed at very low doses, suggesting the involvement of its α2C-adrenoceptor/serotonin 5-HT1A receptor agonism. Therefore, the present investigation suggests that allyphenyline might represent an interesting pharmacological tool to investigate the potential of compounds exhibiting α2C-adrenoceptor/serotonin 5-HT1A receptor agonism and α2A-adrenoceptor antagonism in the treatment of hyperanxiety and hyperlocomotion occurring during alcohol withdrawal in dependent subjects.

Rational site-directed pharmacotherapy for major depressive disorder

It is now accepted that major depressive disorder (MDD) is not a single pathophysiological entity. It is therefore not surprising that remission rates to a first antidepressant trial are low. In addition, antidepressants may target various neuronal elements for which there are gene polymorphisms, such as the serotonin (5-HT) reuptake transporter, which may modulate response. Acting on a single monoaminergic target, such as inhibiting the 5-HT transporter, may confer efficacy in MDD, but other targets may be used and/or combined in treatment-resistant patients. These include the blockade of norepinephrine transporters, monoamine oxidase, 5-HT(2A), 5-HT(1B) and 5-HT7 receptors, and the activation of 5-HT(1A) and dopamine 2 receptors. While antidepressants may have more than one of these properties, so do atypical antipsychotics. When using the latter medications, however, their regimens should be below those effective in treating psychosis to avoid dopamine 2 antagonism, which could be counter-productive in MDD. In some patients, combining medications from treatment initiation may also provide additional therapeutic benefits.

The effect of risperidone on the mirtazapine-induced changes in extracellular monoamines in the rat frontal cortex

BACKGROUND

The aim of our study was to understand the mechanism of clinical efficacy of the combination of an antidepressant and risperidone in drug-resistant depression.

METHODS

We studied the effect of an antidepressant (mirtazapine) and risperidone (atypical antipsychotic), given separately or jointly on extracellular levels of dopamine (DA), serotonin (5-HT) and noradrenaline (NA) in the rat frontal cortex. The animals were given a single intraperitoneal injection of risperidone (1mg/kg) and mirtazapine (10 and 20mg/kg). The release of monoamines in the rat frontal cortex was investigated using a microdialysis in freely moving animals, and monoamine levels were assayed by HPLC with coulochemical detection.

RESULTS

Risperidone increased the cortical extracellular levels of DA, 5-HT and NA. Similarly, mirtazapine dose-dependently increased the cortical extracellular levels of the monoamines studied. A combination of mirtazapine either at the higher dose (20mg/kg) or at both doses (10 and 20mg/kg) with risperidone produced a significant effect on DA and NA release, respectively compared to the effect of any drug given alone. The increase in the DA (but not NA) release induced by mirtazapine plus risperidone was partly blocked by the selective 5-HT1A antagonist WAY 100635 (0.2mg/kg).

CONCLUSIONS

Our data indicate that the increase of cortical extracellular levels of DA and NA by combined administration of mirtazapine and risperidone may be of crucial importance to the pharmacotherapy of drug resistant depression, and that, among other mechanisms, 5-HT1A, 5-HT2A, α2-adrenergic and histamine H1 receptors may play some role in this effect.

Epistasis between 5-HTTLPR and ADRA2B polymorphisms influences attentional bias for emotional information in healthy volunteers

Individual differences in emotional processing are likely to contribute to vulnerability and resilience to emotional disorders such as depression and anxiety. Genetic variation is known to contribute to these differences but they remain incompletely understood. The serotonin transporter (5-HTTLPR) and α2B-adrenergic autoreceptor (ADRA2B) insertion/deletion polymorphisms impact on two separate but interacting monaminergic signalling mechanisms that have been implicated in both emotional processing and emotional disorders. Recent studies suggest that the 5-HTTLPR s allele is associated with a negative attentional bias and an increased risk of emotional disorders. However, such complex behavioural traits are likely to exhibit polygenicity, including epistasis. This study examined the contribution of the 5-HTTLPR and ADRA2B insertion/deletion polymorphisms to attentional biases for aversive information in 94 healthy male volunteers and found evidence of a significant epistatic effect (p<0.001). Specifically, in the presence of the 5-HTTLPR s allele, the attentional bias for aversive information was attenuated by possession of the ADRA2B deletion variant whereas in the absence of the s allele, the bias was enhanced. These data identify a cognitive mechanism linking genotype-dependent serotonergic and noradrenergic signalling that is likely to have implications for the development of cognitive markers for depression/anxiety as well as therapeutic drug effects and personalized approaches to treatment.

Low Doses of Allyphenyline and Cyclomethyline, Effective against Morphine Dependence, Elicit an Antidepressant-like Effect

This study demonstrated that cyclomethyline (2) and the corresponding enantiomers (R)-(-)-2 and (S)-(+)-2, displaying α2C-adrenoreceptor (AR) agonism/α2A-AR antagonism, similarly to allyphenyline (1) and its enantiomers, significantly decreased the naloxone-precipitated withdrawal symptoms in mice at very low doses. It also highlighted that such positive effects on morphine dependence can even be improved by additional serotoninergic 5-HT1A receptor (5-HT1A-R) activation. Indeed, 1 or the single (S)-(+)-1, 2, or both its enantiomers, all behaving as α2C-AR agonists/α2A-AR antagonists/5-HT1A-R agonists, alone and at the same low dose, improved morphine withdrawal syndrome and exerted a potent antidepressant-like effect. Therefore, considering the elevated comorbidity between opiate abuse and depressed mood and the benefit of these multifunctional compounds to both disorders, it is possible that they prove more efficacious and less toxic than a cocktail of drugs in managing opioid addiction.

Effects of sustained administration of quetiapine alone and in combination with a serotonin reuptake inhibitor on norepinephrine and serotonin transmission

Quetiapine is now used in the treatment of unipolar and bipolar disorders, both alone and in combination with other medications. In the current study, the sustained administration of quetiapine and N-Desalkyl quetiapine (NQuet) in rats in a 3 : 1 mixture (hQuetiapine (hQuet)) was used to mimic quetiapine exposure in patients because rats do not produce the latter important metabolite of quetiapine. Sustained administration of hQuet for 2 and 14 days, respectively, significantly enhanced the firing rate of norepinephrine (NE) neurons by blocking the cell body α₂-adrenergic autoreceptors on NE neurons, whether it was given alone or with a serotonin (5-HT) reuptake inhibitor. The 14-day regimen of hQuet enhanced the tonic activation of postsynaptic α₂- but not α₁-adrenergic receptors in the hippocampus. This increase in NE transmission was attributable to increased firing of NE neurons, the inhibition of NE reuptake by NQuet, and the attenuated function of terminal α₂-adrenergic receptors on NE terminals. Sustained administration of hQuet for 2 and 14 days, respectively, significantly inhibited the firing rate of 5-HT, whether it was given alone or with a 5-HT reuptake inhibitor, because of the blockade of excitatory α₁-adrenergic receptors on 5-HT neurons. Nevertheless, the 14-day regimen of hQuet enhanced the tonic activation of postsynaptic 5-HT(1A) receptors in the hippocampus. This increase in 5-HT transmission was attributable to the attenuated inhibitory function of the α₂-adrenergic receptors on 5-HT terminals and possibly to direct 5-HT(1A) receptor agonism by NQuet. The enhancement of NE and 5-HT transmission by hQuet may contribute to its antidepressant action in mood disorders.

Enhancement of serotonergic and noradrenergic neurotransmission in the rat hippocampus by sustained administration of bupropion

RATIONALE

Previous studies reported that bupropion, an effective antidepressant, exerts modulatory actions on serotonin (5-HT) and norepinephrine (NE) neurons.

OBJECTIVES

This study examined effects of bupropion administration on 5-HT and NE neurotransmission in hippocampus.

METHODS

Electrophysiological recordings were obtained from anesthetized Sprague-Dawley rats. Subcutaneously implanted minipumps delivered saline or bupropion (30 mg/kg/day) for 2 and 14 days.

RESULTS

Although sustained bupropion administration did not alter the sensitivity of 5-HT(1A) and α₂-adrenergic receptors, the tonic activation of postsynaptic 5-HT(1A) receptors by endogenous 5-HT was enhanced in 14-day bupropion-treated rats to a greater extent than in the 2-day and control rats, as revealed by the greater disinhibitory action of the 5-HT(1A) antagonist WAY-100635 on hippocampus pyramidal neurons. The function of terminal 5-HT(1B) autoreceptors was not changed as determined by the unaltered effectiveness of different frequencies of stimulation of the ascending 5-HT fibers. The function of α₂-adrenergic receptors on 5-HT terminals was, however, diminished, as indicated by the lesser effect of the α₂-adrenoceptor agonist clonidine. Tonic activation of postsynaptic α₂- and α₁-adrenoceptors by endogenous NE was also increased in 14-day bupropion-treated rats, as indicated by the greater effect of the α₂- and α₁-adrenoceptor antagonists idazoxan and prazosin, respectively, on pyramidal firing. The function of terminal α₂-adrenergic autoreceptors was attenuated since increasing frequency of stimulation of the ascending NE pathway produced a lesser degree of suppression of pyramidal neurons in rats administered bupropion than the control.

CONCLUSION

Enhancement of 5-HT and NE transmissions in hippocampus by prolonged bupropion may account for its effectiveness in major depression.

Locus coeruleus and dorsal raphe neuron activity and response to acute antidepressant administration in a rat model of Parkinson's disease

In addition to noradrenergic and serotonergic systems, dopaminergic neurotransmission seems to play an important role in the aetiopathogenesis of, and recovery from, depression. Moreover, the incidence of depression is higher in patients affected by diseases where the dopaminergic system is highly impaired, such us Parkinson's disease. Here, we investigated the effects of dopamine degeneration on the activity and response to antidepressants of locus coeruleus (LC) noradrenergic and dorsal raphe nucleus (DRN) serotonergic neurons. To this end, single-unit extracellular recordings were performed in control and 6-hydroxydopamine (6-OHDA)-lesioned animals. In this latter group, LC neurons showed a lower basal firing rate as well as less sensitivity to the administration of the serotonin reuptake inhibitor, fluoxetine. The rest of electrophysiological parameters and the response to the administration of the α2-adrenoceptor agonist, clonidine and the noradrenaline reuptake inhibitor, reboxetine remained unaltered. In the DRN, dopamine depletion did not modify the basal electrophysiological characteristics and the response to clonidine or fluoxetine administration. In contrast, the administration of reboxetine more efficiently induced an inhibitory effect in the lesioned group. In additional analyses it was observed that while in control animals, LC and DRN basal firing rate was significantly correlated, this relationship was lost after the 6-OHDA lesion. In conclusion, dopaminergic degeneration alters LC neuron basal activity, the relationship/synteny between both nuclei, and their response to antidepressants. These findings shed fresh light on our understanding of the role of dopamine in depression and the mechanism action of antidepressants.

Association of changes in norepinephrine and serotonin transporter expression with the long-term behavioral effects of antidepressant drugs

Previous work has shown that repeated desipramine treatment causes downregulation of the norepinephrine transporter (NET) and persistent antidepressant-like effects on behavior, ie effects observed 2 days after discontinuation of drug treatment when acute effects are minimized. The present study examined whether this mechanism generalizes to other antidepressants and also is evident for the serotonin transporter (SERT). Treatment of rats for 14 days with 20 mg/kg per day protriptyline or 7.5 mg/kg per day sertraline reduced NET and SERT expression, respectively, in cerebral cortex and hippocampus; these treatments also induced a persistent antidepressant-like effect on forced-swim behavior. Increased serotonergic neurotransmission likely mediated the behavioral effect of sertraline, as it was blocked by inhibition of serotonin synthesis with p-chlorophenylalanine; a parallel effect was observed previously for desipramine and noradrenergic neurotransmission. Treatment with 20 mg/kg per day reboxetine for 42, but not 14, days reduced NET expression; antidepressant-like effects on behavior were observed for both treatment durations. Treatment for 14 days with 70 mg/kg per day venlafaxine, which inhibits both the NET and SERT, or 10 mg/kg per day phenelzine, a monoamine oxidase inhibitor, produced antidepressant-like effects on behavior without altering NET or SERT expression. For all drugs tested, reductions of NET and SERT protein were not accompanied by reduced NET or SERT mRNA in locus coeruleus or dorsal raphe nucleus, respectively. Overall, the present results suggest an important, though not universal, role for NET and SERT regulation in the long-term behavioral effects of antidepressants. Understanding the mechanisms underlying transporter regulation in vivo may suggest novel targets for the development of antidepressant drugs.

Partial neuroprotection with low-dose infusion of the alpha2-adrenergic receptor agonist clonidine after severe hypoxia in preterm fetal sheep

We have previously shown that brief alpha(2)-adrenergic receptor blockade increased neuronal injury after severe hypoxia in preterm fetal sheep. We now examine whether infusion of an alpha(2)-adrenergic receptor agonist, clonidine, is neuroprotective. Preterm fetal sheep (70% gestation) received either saline-vehicle or clonidine at either 10 microg/kg/h (low-dose) or 100 microg/kg/h (high-dose) from 15 min until 4 h after 25 min of umbilical cord occlusion. Both low- and high-dose clonidine infusions after sham-occlusion were associated with transient EEG suppression but no neuronal loss. Low-dose but not high-dose clonidine infusions after umbilical cord occlusion were associated with a significant overall increase in numbers of surviving neurons after three days' recovery. High-dose clonidine was associated with transient hyperglycemia and increased numbers of delayed electrographic seizures. These results provide further evidence that alpha(2)-adrenergic receptor activation shortly after perinatal hypoxia-ischemia can promote neural recovery, but highlight the complex dose-response of exogenous therapy.

Effect of addition of yohimbine (alpha-2-receptor antagonist) to the antidepressant activity of fluoxetine or venlafaxine in the mouse forced swim test

BACKGROUND/AIMS

Studies have suggested that alpha(2)-adrenoceptors strongly affect monoaminergic neurotransmission by enhancing not only noradrenergic but also serotonergic firing rates. With this background in mind, the present study was undertaken to monitor the effect of addition of yohimbine (alpha(2)-adrenoceptor antagonist) to the effect of fluoxetine (selective serotonin reuptake inhibitor) or venlafaxine (dual reuptake inhibitors of both serotonin and norepinephrine) in Porsolt's forced swim test (FST) using male Laca strain mice.

METHOD

The immobility period was recorded in mouse FST during a 6-min period. Different doses of fluoxetine or venlafaxine were administered 30 min before exposing the animals to the test procedure. In the combination study, yohimbine (2 mg/kg i.p.) was administered 15 min before the administration of different doses of fluoxetine or venlafaxine.

RESULTS

Fluoxetine (5, 10, 20 and 40 mg/kg) [F = 28.352] or venlafaxine (2, 4, 8 and 16 mg/kg) [F = 17.842] dose-dependently inhibited the immobility period in mice. Addition of yohimbine (2 mg/kg i.p.) potentiated the antidepressant action of fluoxetine or venlafaxine in mouse FST as the animals showed a decrease in the immobility period compared to the fluoxetine or venlafaxine per se group, respectively.

CONCLUSION

The present study not only demonstrated the association of alpha(2)-receptors in the antidepressant effect of fluoxetine or venlafaxine, but also supports its adjuvant therapy with other antidepressant drugs.

Effect of long-term administration of the antidepressant drug milnacipran on serotonergic and noradrenergic neurotransmission in the rat hippocampus

The effect of a long-term administration of the antidepressant milnacipran on the function of the serotonergic (5-HT) and noradrenergic (NE) systems was studied using single cell recording of CA3 hippocampal pyramidal cells in chloral hydrate-anesthetized male Sprague-Dawley rats, and in vitro [3H]5-HT release measurement from hippocampal slices. The sensitivity of neither the extrasynaptic nor that of the postsynaptic 5-HT1A receptors of the pyramidal neurons was altered, as indicated by their unchanged responsiveness to the microiontophoretic application of 5-HT, and by the unchanged effect of the electrical stimulation at low frequency of the ascending 5-HT bundle, respectively. Increasing the frequency of stimulation (from 1 to 5 Hz) decreased its efficacy in control rats; the milnacipran treatment abolished this phenomenon. This cannot be attributed to a desensitisation of the terminal 5-HT1B autoreceptor, since the suppressive effect of 5-HT agonist 5-carboxyamidotryptamine on [3H]5-HT release was enhanced in milnacipran-treated rats. As for the NE system, the unchanged suppressing effect of microiontophoretic applications of NE and that of the 5 Hz stimulation in the locus coeruleus (LC) on the firing activity of pyramidal neurons indicates that the milnacipran treatment not altered the sensitivity of extrasynaptic alpha2- and postsynaptic alpha1-adrenergic receptors on pyramidal cells, as well as that of the presynaptic alpha2-autoreceptor on NE terminals. The decreased inhibitory effect of NE on the [3H]5-HT release in milnacipran-treated rats revealed that this treatment results in a desensitisation of the presynaptic alpha2-heteroreceptor located on serotonergic terminals. Taken together with the decreased suppressive effect of a low frequency of stimulation of the NE tract, the present results suggest that long-term milnacipran treatment enhances the efficacy of the 5-HT and reduces that of the NE neurotransmission.

Effects of co-administration of antidepressants and monoamine oxidase inhibitors on 5-HT-related behavior in rats

5-hydroxytryptamine (5-HT) syndrome is a dangerous condition of 5-HT excess that can occur during co-administration of a monoamine oxidase (MAO) inhibitor and an antidepressant. We investigated the effects of acute administration of MAO inhibitors and subchronic administration of tricyclic and heterocyclic antidepressants, and a serotonin-noradrenaline reuptake inhibitor (SNRI) on 5-HT syndrome in rats treated with 5-hydroxytryptophan (5-HTP). The irreversible and non-selective MAO inhibitor pargyline, and the reversible and selective MAO-A inhibitor clorgyline, produced increases in 5-HT syndrome in the 5-HTP-treated rats, while subchronic co-administration of imipramine partly intensified and partly attenuated the syndrome, whereas milnacipran only attenuated the syndrome. Co-administration of mianserin partly intensified and partly attenuated the syndrome but the attenuating effect was dominant. Administration of the irreversible and selective MAO-B inhibitor selegiline did not produce any increase in 5-HT syndrome in the 5-HTP-treated rats, compared with the saline control. These data suggest that non-selective MAO and selective MAO-A inhibitors can induce 5-HT syndrome in humans when co-administered with antidepressants. Furthermore, the risk of 5-HT syndrome may be lower with the selective MAO-B inhibitor selegiline.

Differential noradrenergic influence on seizure expression in genetically Fast and Slow kindling rat strains during massed trial stimulation of the amygdala

The involvement of alpha(2) noradrenergic receptors during amygdala 'massed' stimulation (MS) was examined in rats that were selectively bred to be seizure-prone (Fast) or seizure-resistant (Slow) to amygdala kindling. The selective alpha(2) noradrenergic agonist guanfacine, or the antagonist idazoxan, was intraperitoneally injected during the MS procedure to study subsequent changes in afterdischarge (AD) threshold, AD duration and behavioral seizure expression. These measurements were again assessed weekly for 2 weeks after the MS treatment. Daily kindling began immediately thereafter. Following 6 stage-5 once daily convulsive seizures, guanfacine or idazoxan were re-administered. With idazoxan, the Slow rats expressed greater numbers of convulsive seizures and longer AD durations compared to guanfacine or saline controls during MS treatment. This pro-convulsive property of idazoxan was absent in Fast rats. By contrast, Fast rats showed enhanced convulsive expression in the presence of guanfacine. In the fully kindled rat, idazoxan and guanfacine differentially impacted seizure duration and severity in the Slow rats, but again not in the Fast rats. These data suggest that some aspect(s) of the alpha(2) noradrenergic system in the Fast and Slow rats are dissimilar and the mechanisms by which these receptors govern seizure genesis and propagation may be genetically controlled and distinct.

A comparison of the chronic treatment effects of venlafaxine and other antidepressants on serotonin and norepinephrine transporters

BACKGROUND

Venlafaxine blocks both serotonin and norepinephrine transporters (SERT and NET), with higher affinity for SERT. Serotonergic effects occur with lower doses, whereas both serotonergic and noradrenergic effects occur with higher doses of venlafaxine. Chronic treatment of rats with selective serotonin reuptake inhibitors decreases SERT binding sites, whereas similar treatment with selective norepinephrine reuptake inhibitors decreases NET binding sites. We hypothesized that venlafaxine would affect monoamine transporters dose-dependently, with low doses causing selective reduction of SERT binding sites and higher doses reducing both SERT and NET binding sites.

METHODS

Rats were treated for 21 days with a low (15 mg/kg/day) or high (70 mg/kg/day) dose of venlafaxine, vehicle, or other antidepressants. The SERT and NET density was determined by quantitative autoradiography.

RESULTS

Neither dose of venlafaxine nor amitriptyline reduced binding to either the SERT or NET. In rats with noradrenergic terminals destroyed by 6-hydroxydopamine, venlafaxine still failed to reduce SERT binding. Also, rats treated simultaneously with sertraline plus desipramine exhibited reductions in both SERT and NET binding.

CONCLUSIONS

Chronic venlafaxine treatment affected SERT and NET binding differently from paroxetine or desipramine. The inability of venlafaxine to reduce SERT or NET binding sites is not due to its dual uptake inhibiting properties.

Uptake and release of norepinephrine by serotonergic terminals in norepinephrine transporter knock-out mice: implications for the action of selective serotonin reuptake inhibitors

Our aim was to investigate the functional properties of the noradrenergic system in genetically modified mice lacking the norepinephrine transporter (NET). We measured the uptake and release of [(3)H]norepinephrine ([(3)H]NE) from hippocampal and cortical slices of NET(-/-) knock-out (KO) and NET(+/+) wild-type (WT) mice and investigated the presynaptic alpha2-adenoceptor-mediated modulation of NE release in vitro and in vivo. The [(3)H]NE uptake was reduced to 12.6% (hippocampus) and 33.5% (frontal cortex) of WT control in KO mice. The neuronal component of this residual uptake was decreased by 79.4 and 100%, respectively, when a selective serotonin reuptake inhibitor (SSRI) citalopram was present during the loading. The more preserved neuronal release of [(3)H]NE (hippocampus, 28.1%; frontal cortex, 74.4%; compared with WT) almost completely disappeared in both regions (94.1 and 95.3% decrease compared with KO, respectively) in the presence of citalopram, suggesting that [(3)H]NE was taken up and released by serotonergic varicosities. This was further supported by the finding that the release of [(3)H]NE from hippocampal slices of KO mice was not modulated by the alpha2-adrenoceptor antagonist 7,8-(methylenedioxy)-14-alpha-hydroxyalloberbane HCl, whereas the endogenous release of NE measured by microdialysis was even more efficiently enhanced by this drug in NET-deficient mice. These experiments indicate that serotonergic varicosities can accumulate and release NE as a result of the heterologous uptake of transmitters. Because the diffusion of NE may be spatially limited by serotonin transporters, the SSRIs, despite their selectivity, might enhance not only serotonergic but also noradrenergic neurotransmission, which might contribute to their antidepressant action.

The cognitive paradox in posttraumatic stress disorder: a hypothesis

Posttraumatic stress disorder (PTSD) is characterized by a peculiar cognitive state. The traumatic event(s) are partly hypermemorized, partly blurred, whereas the ability to store and retrieve new information is impaired. The question is raised as to what the biological systems might be that 'carry' this cognitive paradox. Four possible candidate systems are discussed. It is concluded that understimulation of the corticosteroid receptors, particularly the glucocorticoid receptors (GRs), overactivity of the noradrenaline (NA) and vasopressin (VA) systems, and deficits in the 5-Hydroxytryptamine (5-HT) system, particularly the 5-HT(1A) system, could generate a cognitive syndrome similar to the one observed in PTSD. A dual hypothesis is launched holding that (a) in PTSD, downregulation of the 5-HT(1A) receptor system is the primary lesion, while the other dysfunctions mentioned are subsidiaries and that (b) underdevelopment of or damage to the 5-HT(1A) receptor system will make a person PTSD-prone.

Addition of the alpha2-antagonist yohimbine to fluoxetine: effects on rate of antidepressant response

Electrophysiological studies suggest that alpha2-adrenoceptors profoundly affect monoaminergic neurotransmission by enhancing noradrenergic tone and serotonergic firing rates. Recent reports suggest that alpha2-antagonism may hasten and improve the response to antidepressant medications. To test this hypothesis, a randomized double-blind controlled trial was undertaken to determine if the combination of an alpha2-antagonist (yohimbine) with a selective serotonin reuptake agent (SSRI) (fluoxetine) results in more rapid onset of antidepressant action than an SSRI agent alone. In all, 50 subjects with a DSM-IV diagnosis of major depressive disorder confirmed by SCID interview were randomly assigned to receive either fluoxetine 20 mg plus placebo (F/P) or fluxetine 20 mg plus a titrated dose of yohimbine (F/Y). The yohimbine dose was titrated based on blood pressure changes over the treatment period, in a blind-preserving manner. Hamilton depression scale ratings (HDRS) and clinical global impression (CGI) ratings were obtained weekly over a period of 6 weeks. The rate of achieving categorical positive responses was significantly more rapid in the F/Y group compared to the F/P group using both the HDRS and the CGI scales as outcome measures in a survival analysis using a log-rank test (chi2(1) = 5.86, p = 0.016 and chi2(1) = 5.29, p = 0.021, respectively). At the last observed visit, 18 (69%) of the 26 F/Y subjects met the response criteria for CGI compared to 10 (42%) of 24 F/P subjects. Using the HDRS criteria, 17 (65%) of 26 F/Y subject vs 10 (42%) of 24 F/P subjects were responders. The addition of the alpha2-antagonist yohimbine to fluoxetine appears to hasten the antidepressant response. There is also a trend suggesting an increased percentage of responders to the combined treatment at the end of the 6-week trial.

Maternal separation in rats leads to anxiety-like behavior and a blunted ACTH response and altered neurotransmitter levels in response to a subsequent stressor

Adverse early life experiences can have a negative impact on behavior later in life. We subjected rat pups to maternal separation and determined the effect's thereof on adult behavior. We removed rat pups from their mothers for 3 h daily from postnatal days 2 to 14. While controls were reared normally on day 60, the behaviors of the rats were tested using the elevated plus-maze. Some rats were subsequently subjected to restraint stress for a 10-min period. Trunk blood was collected for basal, as well as 15- and 60-min postrestraint stress ACTH determinations. Neurotransmitter levels (noradrenaline (NA), serotonin (5HT), and their metabolites, MHPG and 5HIAA, respectively) were also determined at basal, immediately and 15-min post-restraint stress in the hypothalamus, hippocampus, and frontal cortex in another group of animals. The amount of entries into the arms of the elevated plus-maze was significantly reduced in the separated animals, indicating decreased locomotion. They spent significantly more time in the closed arms of the maze. A significant increase in defecation frequency was noted. These observations suggested anxious behavior. Basal ACTH levels were significantly higher in separated animals. At 15-min post-restraint stress, the ACTH levels were significantly lower than controls, indicating a blunted stress response. A decrease in noradrenaline was noted first in limbic regions and an increase in 5HIAA levels was found in the frontal cortex and hippocampus. We conclude that maternal separation induced abnormal behaviors and stress responses that were associated with altered neurotransmitter levels.

Modulation of theta rhythmicity in the medial septal neurons and the hippocampal electroencephalogram in the awake rabbit via actions at noradrenergic alpha2-receptors

The modulation of the firing discharge of medial septal neurons and of the hippocampal electroencephalogram (EEG) mediated by actions on alpha2-adrenoreceptors (ARs) was investigated in awake rabbits. Bilateral i.c.v. infusion of a relatively low dose (0.5 microg) of the alpha2-AR agonist clonidine produced a reduction in the theta rhythmicity of both medial septal neurons and the hippocampal EEG. In contrast, a high dose of clonidine (5 microg) increased the percentage and degree of rhythmicity of theta bursting medial septal neurons as well as the theta power of the hippocampal EEG. On the other hand, administration of alpha2-AR antagonist idazoxan produced the opposite dose-dependent effect. While a low dose of the antagonist (20 microg) produced an increase in both the theta rhythmicity of medial septal neurons and the theta power of the hippocampal EEG, a high dose (100 microg) caused a reduction of theta rhythmicity in both the medial septum and hippocampus. These results suggest that low doses of alpha2-ARs agents may act at autoreceptors regulating the synaptic release of noradrenaline, while high doses of alpha2-ARs drugs may have a predominant postsynaptic action. Similar results were observed after local injection of the alpha2-AR drugs into the medial septum suggesting that the effects induced by the i.c.v. infusion were primarily mediated at the medial septal level. We suggest that noradrenergic transmission via the postsynaptic alpha2-ARs produces fast and strong activation of the septohippocampal system in situations that require urgent selective attention to functionally significant information (alert, aware), whereas the action via the presynaptic alpha2-ARs allows a quick return of the activity to the initial level.

Zuclopenthixol facilitates memory retrieval in rats: possible involvement of noradrenergic and serotonergic mechanisms

Although disturbed memory function often coexists with psychosis, the cognitive effects of antipsychotic medications with diverse pharmacodynamic properties are rarely investigated. The neurocognitive profile of zuclopenthixol, a thioxanthene dopaminergic antagonist and a conventional neuroleptic agent, has yet to be investigated despite the effect of the drug on a variety of neurotransmitter systems involved in mediation of learning and memory processes. In this study, the effect of zuclopenthixol was tested on memory retrieval 24 h after training using an inhibitory avoidance task in rats. Acute administration of zuclopenthixol (0.7 and 1.4 mg/kg i.p.) before retrieval testing increased step-through latency during the test session. The same doses of zuclopenthixol did not affect the ambulatory activity of rats in the openfield test and therefore the facilitatory effect of the drug on memory function could not be confounded with any motoric properties. This study also investigated the effect of zuclopenthixol on cortical and hippocampal monoaminergic neurotransmitters' levels together with acetylcholinesterase enzyme (AChE) activity, both of which are known to be important in control of cognitive function. Administration of zuclopenthixol (0.7 and 1.4 mg/kg i.p.) neither affected dopamine (DA) level nor AChE activity in rat cortex and hippocampus. On the other hand, the lower dose of zuclopenthixol elevated cortical norepinephrine (NE) level, while the higher dose elevated both cortical and hippocampal NE level together with hippocampal serotonin (5-HT) level. These results may suggest the involvement of adrenergic and serotonergic mechanisms in the facilitatory effect of zuclopenthixol on retrieval memory. Zuclopenthixol may therefore be a better alternative than other commonly used antipsychotic medications reported to impair cognitive function of schizophrenic patients.

Interleukin 1alpha alters hippocampal serotonin and norepinephrine release during open-field behavior in Sprague-Dawley animals: differences from the Fawn-Hooded animal model of depression

Detection of two biogenic amine neurotransmitters, serotonin (5-HT) and norepinephrine (NE) within the CA1 region of the hippocampus (HPC) of behaving male laboratory animals (Rattus norvegicus), was performed with miniature carbon sensors (BRODERICK PROBES) and in vivo semidifferential microvoltammetry after acute administration of the soluble immune factor, human recombinant, interleukin (IL) 1alpha (10 and 100 ng/kg i.p.). Two animal models were compared, i.e., (a) the Sprague-Dawley (SD) model, a strain neither biochemically nor immune-challenged and (b) the Fawn-Hooded (FH) model, a biochemically (5-HT-deficient) and immune-challenged animal. Open-field behaviors, locomotion (ambulations) and stereotypy (fine movements of sniffing and grooming) were monitored with infrared photobeams while 5-HT and NE were selectively and separately detected within seconds in real time. Subchronic studies were performed in the same animals 24 h later at which time no further drug was administered. Results from acute treatment studies showed that IL-1alpha altered HPC monoamines and behavior viz-a-viz habituation values (baseline) in the SD strain differently from those in the FH strain as follows: (1) although 5-HT release was significantly increased within CA1 region of HPC in both SD and FH strains (P<.0001), the extent of the HPC 5-HT increase in the 5-HT-deficient FH strain was significantly less than that of the SD strain at both doses (P<.0001). The subchronic studies showed that 5-HT release within the HPC in the SD strain significantly increased (135%) over drug treatment values (P<.001), whereas HPC 5-HT release in the FH strain remained the same as that seen in the acute drug treatment studies; the difference between strains for the subchronic study was also statistically significant (P<.01). (2) IL-1alpha significantly decreased HPC NE release in the SD strain (P<.0004) while IL-1alpha decreased HPC NE release in the FH strain only at the 10-ng/kg dose (P<.001); at the 100-ng/kg dose in the FH strain, NE rebounded towards baseline and increased 15% above baseline reaching statistical significance (P<.05). Subchronic studies in the SD strain showed a further decreased NE signal to 38% below baseline (P<.0001), whereas subchronic studies in the FH strain showed a significant increase in NE release (P<.02). The difference between strains in the subchronic NE studies was significant (P<.001). (3) Ambulations were increased after IL-1alpha administration in acute studies in both the SD and the FH strains, but the increase did not reach statistical significance, whereas in the subchronic studies, both strains exhibited significant increases as revealed by post hoc analyses (P<.05). There was a statistically significant difference between strains in acute studies (P<.001), whereas no significant differences between models were seen in ambulation behavior in subchronic studies. (4) Fine movements increased over baseline after IL-1alpha administration in both animal models in acute studies, however, results did not reach statistical significance, likely due to the episodic effect of IL-1alpha on movement behavior in both the SD and the FH strains. However, the SD strain showed a significant increase in fine movement behavior during the subchronic studies (P<.02). Significant differences in fine movements between animal models were not observed either acutely or in subchronic studies. In summary, the data show that immune modulation by IL-1alpha affects HPC neurochemistry and behavior in SD versus FH animal models differently and/or to different degrees. The data show that while the FH animal model is subsensitive to 5-HT agonists, 5-HT function can be stimulated. Comparison of genetically diverse animal models provides a reliable means to identify and discern cytokine-induced depressive versus stressor properties. Selective sensor technology provides a powerful tool as movement behavior is monitored and interpreted as a function of monoamine neurotransmission.

In the rat forced swimming test, chronic but not subacute administration of dual 5-HT/NA antidepressant treatments may produce greater effects than selective drugs

The rat forced swimming test (FST) distinguishes selective serotonin (5-HT) and selective noradrenaline (NA) reuptake-inhibitors, which respectively increase swimming and climbing behaviours. However, NA-system-mediated inhibition of 5-HT-induced swimming prevents dual 5-HT/NA reuptake-inhibition to produce concurrently climbing with swimming. Since adaptative neurochemical processes occur in the treatment of depression, we examined the influence of long-term antidepressant treatment on these interactions.

METHODS

(1) Selective [fluoxetine: 10 mg/kg; desipramine: 10 mg/kg] and non-selective [milnacipran: 40 mg/kg; mirtazapine: 20 mg/kg] antidepressants were administered subacutely (3inj) and chronically (17inj) over 16 days. (2) A subacute fluoxetine-desipramine combination (10-10 mg/kg) was administered in rats that were pre-treated with chronic-desipramine (10 mg/kg per day, 14 days). (3) NA-system-mediated interactions were further examined by combining the alpha(2)-receptor agonist clonidine (5, 10, 20, 200 microg/kg) with 10 mg/kg fluoxetine.

RESULTS

(1) Long-term treatment with either fluoxetine or desipramine does not modify the behavioural response produced by their subacute administration. (2) In contrast, whereas subacute-milnacipran increases climbing solely, chronic-milnacipran produces greater anti-immobility effects and increases both climbing and swimming behaviours. Similarly, the fluoxetine-desipramine combination produces climbing solely, but increases both climbing and swimming behaviours in animals pre-treated with chronic-desipramine. Chronic but not subacute-mirtazapine increases swimming behaviour. (3) clonidine dose-dependently antagonizes fluoxetine-induced anti-immobility effects and swimming behaviour.

CONCLUSIONS

Chronic enhancement of NA-transmission alters NA-system-mediated inhibition of 5-HT-induced behaviour in the FST, which may involve alpha(2)-receptors.

Effect of the selective noradrenergic reuptake inhibitor reboxetine on the firing activity of noradrenaline and serotonin neurons

Reboxetine is a non-tricyclic antidepressant with selective noradrenergic (NA) reuptake-blocking effects. The effects of acute and sustained administration of reboxetine, on the firing activity of locus coeruleus NA neurons and dorsal raphe 5-HT neurons, were assessed using in vivo extracellular unitary recording in rats anaesthetized with chloral hydrate. Reboxetine (0.1-1.25 mg/kg, i.v.) dose-dependently decreased the firing activity of NA neurons (ED50 = 480 +/- 14 microg/kg). A 2-day treatment with reboxetine at 1.25, 2.5, 5, or 10 mg/kg per day (using osmotic minipumps implanted subcutaneously) produced significant decreases of 52%, 68%, 81%, and 83%, respectively, of NA firing activity. When the reboxetine treatment (2.5 mg/kg per day) duration was prolonged to 7 days, a 66% decrease in NA firing activity was observed which further decreased to 80% after 21 days of treatment. In contrast, 5-HT neuron firing rate remained unaltered following short- and long-term reboxetine treatments. The suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of NA neurons was unchanged in long-term reboxetine-treated rats, but its effect on the firing activity of 5-HT neurons was blunted. The enhancement of NA firing activity by the 5-HT1A agonist 8-OH-DPAT was abolished in long-term reboxetine-treated rats, whereas, the inhibitory effect of the 5-HT2 agonist DOI was attenuated by about three-fold. In conclusion, sustained NA reuptake blockade by reboxetine lead to profound alterations in the function of NA neurons and of 5-HT receptors modulating their firing activity.

Monoamine neurotransmitters in resected hippocampal subparcellations from neocortical and mesial temporal lobe epilepsy patients: in situ microvoltammetric studies

It is known that epilepsy patients diagnosed with neocortical temporal lobe epilepsy (NTLE), differ from those diagnosed with mesial temporal lobe epilepsy (MTLE), e.g., in hippocampal (HPC) pathology. In the present studies, we tested the hypothesis that NTLE and MTLE subtypes of human epilepsy might differ in regards to their HPC monoamine neurochemistry. Monoamine neurotransmitters were studied in separate signals and within s with semiderivative microvoltammetry, used in combination with stearate indicator, Ag-AgCl reference and stainless steel auxiliary microelectrodes. Anterior HPC specimens from the patients' epileptogenic zone, defined by electrocorticography, were resected neurosurgically from 13 consecutive patients with intractable temporal lobe epilepsy. Four patients were diagnosed with NTLE and nine with MTLE. The criteria for the diagnosis of NTLE versus MTLE was absence versus presence of HPC sclerosis, respectively, based on MRI examination of resected tissue. In addition, NTLE patients demonstrated seizure onset in anterolateral temporal neocortex on electroencephalography (EEG). HPC subparcellations studied were: (a) Granular Cells of the Dentate Gyrus (DG), (b) Polymorphic Layer of DG and (c) Pyramidal Layer: subfields, CA1 and CA2. Dopamine (DA), serotonin (5-HT), norepinephrine (NE) and ascorbic acid (AA) (co-factor in DA to NE synthesis), exhibited separate and characteristic half-wave potentials in millivolts. Each half-wave potential, i.e., the potential at which maximum current was generated, was experimentally established in vitro. Concentrations of neurotransmitters found in HPC subparcellations were interpolated from calibration curves derived in vitro from electrochemical detection of monoamines and AA in saline phosphate buffer. Significant differences between subtypes in concentration of monoamines were analyzed by the Mann Whitney rank sum test and those differences in probability distribution of monoamines were analyzed by the Fisher Exact test; in each case, P<0.01 was the criteria selected for determining statistical significance. DA concentrations were higher in NTLE compared with MTLE in each HPC subparcellation [P=0.037, 0.024 and 0.007, respectively (P<0.01)] and DA occurred more frequently in NTLE in the Pyramidal Layer [P=0.077 (P<0.01)]. AA was present in one NTLE patient. NE concentrations were higher in MTLE vs. NTLE in each subparcellation [P=0.012, 0.067 and 0.07, respectively (P<0.01)] and NE occurred more frequently in MTLE in Granular Cells of DG and Pyramidal Layer [P=0.052 and 0.014, respectively (P<0.01)]. In MTLE, NE concentrations in the CA1 subfield of the Pyramidal Layer were decreased vs. the CA2 subfield [P=0.063 (P<0.01)]. Serotonin was found in every HPC subparcellation of each subtype but 5-HT concentrations were higher in NTLE vs. MTLE in the Granular Cells of DG and the Pyramidal Layer (CA1 subfield) [P=0.076 and 0.095, respectively (P<0.01)]. Thus, this preliminary study showed that marked differences in HPC monoamine neurochemistry occurred in NTLE patients as compared with MTLE patients.

Effects of sustained administration of the serotonin and norepinephrine reuptake inhibitor venlafaxine: II. In vitro studies in the rat

The effects of long-term administrations of a low (10 mg/kg/day) and a high (40 mg/kg/day) dose of the dual 5-HT and NE reuptake inhibitor venlafaxine (delivered s.c. by osmotic minipumps for 21 days) were assessed on the electrically-evoked release of tritium from hippocampal slices preloaded with either [(3)H]5-HT or [(3)H]NE, 48 h after the removal of the minipump. The high, but not the low, dose regimen of venlafaxine enhanced the electrically-evoked release of [(3)H]5-HT while treatment with the high dose of venlafaxine failed to alter the electrically-evoked release of [(3)H]NE. The inhibitory effect of the 5-HT(1B) agonist CP 93,129 on the electrically evoked release of [(3)H]5-HT was unaltered by the low dose regimen of venlafaxine while it was attenuated in rats treated with the high dose of venlafaxine, indicative of a functional desensitization of the terminal 5-HT(1B) autoreceptor. Unexpectedly, neither regimen of venlafaxine altered the inhibitory effect of UK 14,304 on the electrically evoked release of both [(3)H]5-HT and [(3)H]NE, indicating that neither the alpha(2)-adrenergic auto- nor heteroreceptors were desensitized. Finally, the functions of the 5-HT and NE reuptake process were assessed. None of the treatment regimens altered the basal uptake of [(3)H]5-HT from hippocampal or mesencephalic slices nor that of [(3)H]NE from hippocampal slices. Finally, the enhancing effect of 1 microM of paroxetine in the perfusion medium on the electrical release of [(3)H]5-HT was unaltered in hippocampal slices prepared from rats that had been treated for 21 days with 40 mg/kg/day of venlafaxine. Taken together, these results indicate that, in terms of alteration of the sensitivity of the terminal 5-HT(1B) autoreceptor, alpha(2)-adrenergic auto-and heteroreceptors, the effects of long-term administration of venlafaxine are no different than those observed with classical SSRI's.

Reciprocal autoreceptor and heteroreceptor control of serotonergic, dopaminergic and noradrenergic transmission in the frontal cortex: relevance to the actions of antidepressant agents

The frontal cortex (FCX) plays a key role in processes that control mood, cognition and motor behaviour, functions which are compromised in depression, schizophrenia and other psychiatric disorders. In this regard, there is considerable evidence that a perturbation of monoaminergic input to the FCX is involved in the pathogenesis of these states. Correspondingly, the modulation of monoaminergic transmission in the FCX and other corticolimbic structures plays an important role in the actions of antipsychotic and antidepressant agents. In order to further understand the significance of monoaminergic systems in psychiatric disorders and their treatment, it is essential to characterize mechanisms underlying their modulation. Within this framework, the present commentary focuses on our electrophysiological and dialysis analyses of the complex and reciprocal pattern of auto- and heteroreceptor mediated control of dopaminergic, noradrenergic and serotonergic transmission in the FCX. The delineation of such interactions provides a framework for an interpretation of the influence of diverse classes of antidepressant agent upon extracellular levels of dopamine, noradrenaline and serotonin in FCX. Moreover, it also generates important insights into strategies for the potential improvement in the therapeutic profiles of antidepressant agents.

Mirtazapine enhances frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission by blockade of alpha2-adrenergic and serotonin2C receptors: a comparison with citalopram

Mirtazapine displayed marked affinity for cloned, human alpha2A-adrenergic (AR) receptors at which it blocked noradrenaline (NA)-induced stimulation of guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]-GTPgammaS) binding. Similarly, mirtazapine showed high affinity for cloned, human serotonin (5-HT)2C receptors at which it abolished 5-HT-induced phosphoinositide generation. Alpha2-AR antagonist properties were revealed in vivo by blockade of UK-14,304-induced antinociception, while antagonist actions at 5-HT2C receptors were demonstrated by blockade of Ro 60 0175-induced penile erections and discriminative stimulus properties. Mirtazapine showed negligible affinity for 5-HT reuptake sites, in contrast to the selective 5-HT reuptake inhibitor, citalopram. In freely moving rats, in the dorsal hippocampus, frontal cortex (FCX), nucleus accumbens and striatum, citalopram increased dialysate levels of 5-HT, but not dopamine (DA) and NA. On the contrary, mirtazapine markedly elevated dialysate levels of NA and, in FCX, DA, whereas 5-HT was not affected. Citalopram inhibited the firing rate of serotonergic neurons in dorsal raphe nucleus, but not of dopaminergic neurons in the ventral tegmental area, nor adrenergic neurons in the locus coeruleus. Mirtazapine, in contrast, enhanced the firing rate of dopaminergic and adrenergic, but not serotonergic, neurons. Following 2 weeks administration, the facilitatory influence of mirtazapine upon dialysate levels of DA and NA versus 5-HT in FCX was maintained, and the influence of citalopram upon FCX levels of 5-HT versus DA and NA was also unchanged. Moreover, citalopram still inhibited, and mirtazapine still failed to influence, dorsal raphe serotonergic neurons. In conclusion, in contrast to citalopram, mirtazapine reinforces frontocortical dopaminergic and corticolimbic adrenergic, but not serotonergic, transmission. These actions reflect antagonist properties at alpha2A-AR and 5-HT2C receptors.

Effect of sustained administration of the 5-HT1A receptor agonist flesinoxan on rat 5-HT neurotransmission

A short-term treatment with flesinoxan (2.5 and 5 mg/kg/day x 2 days, s.c., delivered using osmotic minipumps) decreased significantly the spontaneous firing activity of dorsal raphe serotonin (5-HT) neurons of male Sprague-Dawley rats. This firing was still decreased following 1 week of treatment with flesinoxan (5 mg/kg/day) but was back to normal after a treatment of 2 weeks. This recovery of firing was associated with a 3-fold shift to the right of the dose-response curve of the effect of the 5-HT autoreceptor agonist lysergic acid diethylamide on the firing activity of 5-HT neurons, indicating a desensitization of somatodendritic 5-HT1A autoreceptors. At the postsynaptic level, long-term treatment with flesinoxan (5 mg/kg/day x 14 days) did not modify the responsiveness of dorsal hippocampus CA3 pyramidal neurons to microiontophoretic applications of 5-HT and flesinoxan nor to endogenous 5-HT released by the electrical stimulation of the ascending 5-HT pathway, indicating an unchanged sensitivity of postsynaptic 5-HT1A receptors. Finally, in rats treated with flesinoxan for 2 weeks, the administration of the selective 5-HT1A receptor antagonist (N-{2-[4(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)cyclohe xanecarboxamide trihydroxychloride (WAY 100635, 100 and 500 microg/kg, i.v.) did not increase the firing activity of dorsal hippocampus CA3 pyramidal neurons, thus failing to reveal an enhanced tonic activation of postsynaptic 5-HT1A receptors as for other antidepressant drugs, including the 5-HT1A receptor agonist gepirone. The marked potency and the long dissociation constant of flesinoxan for the 5-HT1A receptors may account for the latter discrepancy. In conclusion, as for selective 5-HT re-uptake inhibitors, monoamine oxidase inhibitors and 5-HT1A receptor agonists, flesinoxan produced most of the adaptive changes exerted by these antidepressant drugs on the 5-HT system.

Pindolol and mianserin augment the antidepressant activity of fluoxetine in hospitalized major depressed patients, including those with treatment resistance

The aims of this study were to examine whether pindolol, a serotonin (5-hydroxytryptamine [5-HT])-1A receptor antagonist, and mianserin, a 5-HT2A/C and alpha2-adrenoceptor (alpha2-AR) antagonist, may augment the clinical efficacy of fluoxetine, a selective serotonin reuptake inhibitor, and shorten the latency of onset of antidepressive activity in the treatment of major and treatment-resistant depression (TRD). Ten days after admission to the hospital, 31 major depressed patients were randomly assigned using a double-blind, controlled design to receive fluoxetine 20 mg daily, fluoxetine 20 mg daily plus pindolol 7.5 mg daily, or fluoxetine 20 mg plus mianserin 30 mg daily for 5 weeks. The 17-item Hamilton Rating Scale for Depression (HAM-D) score was the primary outcome measure. Analysis of efficacy was conducted according to the intent-to-treat analysis principle considering the change from baseline to endpoint. It was found that fluoxetine plus pindolol and fluoxetine plus mianserin were significantly more effective than fluoxetine alone. Using an outcome measure of 50% reduction in the HAM-D, a 60% response rate was found in patients treated with either fluoxetine plus pindolol or fluoxetine plus mianserin compared with a 9% response rate in patients treated with fluoxetine alone. The HAM-D score 1 week after starting fluoxetine plus mianserin decreased more than 4 points and was significantly greater than that obtained by fluoxetine alone. The results suggest that pindolol and mianserin augment the efficacy of fluoxetine in the treatment of TRD and that mianserin, but not pindolol, may significantly shorten the latency of onset of antidepressive action when combined with fluoxetine.

Diurnal variation in 5-HT1B autoreceptor function in the anterior hypothalamus in vivo: effect of chronic antidepressant drug treatment

1. Intracerebral microdialysis was used to examine the function of the terminal 5-hydroxytryptamine (5-HT) autoreceptor in the anterior hypothalamus of anaesthetized rats at two points in the light phase of the light-dark cycle. 2. Infusion of the 5-HT1A/1B agonist 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (RU24969) 0.1, 1.0 and 10 microM through the microdialysis probe led to a concentration-dependent decrease (49, 56 and 65% respectively) in 5-HT output. The effect of RU24969 (1 and 5 microM) was prevented by concurrent infusion of methiothepin (1 and 10 microM) into the anterior hypothalamus via the microdialysis probe. Infusion of methiothepin alone (1.0 and 10 microM) increased (15 and 142% respectively) 5-HT output. 3. Infusion of RU24969 (5 microM) through the probe at mid-light and end-light resulted in a quantitatively greater decrease in 5-HT output at end-light compared with mid-light. 4. Following treatment with either paroxetine hydrochloride (10 mg kg(-1) i.p.) or desipramine hydrochloride (10 mg kg)(-1) i.p.) for 21 days the function of the terminal 5-HT1B autoreceptor was more markedly attenuated at end-light. 5. The data show that, as defined by the response to RU24969, the function of the 5-HT1B receptors that control 5-HT output in the anterior hypothalamus is attenuated following chronic desipramine or paroxetine treatment in a time-of-day-dependent manner.

Neurochemistry and pharmacology of the major hippocampal transmitter systems: synaptic and nonsynaptic interactions

Hippocampus plays a crucial role in important brain functions (e.g. memory, learning) thus in the past two decades this brain region became a major objective of neuroscience research. During this period large number of anatomical, neurochemical and electrophysiological data have been accumulated. While excellent reviews have been published on the anatomy and electrophysiology of hippocampal formation, the neurochemistry of this area has not been thoroughly surveyed. Therefore the aim of this review is to summarize the neurochemical and pharmacological data on the release of the major neurotransmitters found in the hippocampal region: glutamate (GLU), gamma-amino butyric acid (GABA), acetylcholine (ACh), noradrenaline (NA) and serotonin (5-HT). In addition, this review analyzes the synaptic and nonsynaptic interactions between hippocampal neuronal elements and overviews how auto- and heteroreceptors are involved in the presynaptic modulation of transmitter release. The presented data clearly show that transmitters released from axon terminals without synaptic contact play an important role in the fine tuning of communication between neurons within a neuronal circuit.

Acute and long-term actions of the antidepressant drug mirtazapine on central 5-HT neurotransmission

Mirtazapine (ORG 3770, Remeron) is a new alpha 2-adrenoceptor antagonist which has been shown to be an effective antidepressant drug. The aims of the studies were to assess, using an in vivo electrophysiological paradigm in the rat, the effects of acute and long-term treatment with mirtazapine on pre- and postsynaptic alpha 2-adrenoceptors and to determine whether this drug could modulate serotonin (5-HT) neurotransmission. Acute administration of mirtazapine produced a transient increase of the firing activity of dorsal raphe 5-HT neurons. This effect was mediated via norepinephrine (NE) neurons because it was abolished in NE-lesioned rats. In fact, this increased firing rate of 5-HT neurons was due to their activation by the enhanced release of NE resulting from the blockade of alpha 2-adrenergic autoreceptors of locus coeruleus neurons. Furthermore, acute mirtazapine injection transiently enhanced the firing activity of locus coeruleus NE neurons and attenuated the suppressant effect of the alpha 2-adrenoceptor agonist clonidine on these NE neurons. Sustained administration of mirtazapine for 21 days (5 mg/kg/day, s.c., using minipumps) lead to a marked increase in the firing rate of 5-HT neurons (75%) but a more modest increase in the firing rate of NE neurons (30%), as well as to a desensitization of alpha 2-adrenergic heteroreceptors on 5-HT terminals in the hippocampus. The desensitization of these heteroreceptors, resulting from an increased synaptic availability of NE induced by mirtazapine would free 5-HT terminals from the inhibitory influence of NE on 5-HT release. These modifications of 5-HT neurons lead to an increased tonic activation of postsynaptic 5-HT1A receptors. The latter conclusion was based on the capacity of the selective 5-HT1A receptor antagonist WAY 100635 to enhance the firing activity of dorsal hippocampus CA3 pyramidal neurons in mirtazapine-treated rats but not in controls. This enhanced 5-HT neurotransmission may underlie to the antidepressant effect of mirtazapine.

Clonidine potentiates the effects of 5-HT1A, 5-HT1B and 5-HT2A/2C antagonists and 8-OH-DPAT in the mouse forced swimming test

The present study was undertaken to identify the receptor subtypes involved in clonidine's ability to enhance the effects of antidepressant drugs in the mouse forced swimming test. Clonidine (0.06 mg/kg, i.p.) significantly enhanced the antidepressant-like effects of subactive doses of the 5-HT1A receptor agonist, 8-OH-DPAT (1 mg/kg, i.p.; P<0.01); the 5-HT1A receptor antagonist, NAN 190 (0.5 mg/kg, i.p.; P<0.01); the 5-HT1A/1B autoreceptor antagonist, (+/-) pindolol (32 mg/kg, i.p.; P<0.01); the 5-HT2A/2C receptor antagonist, ritanserin (4 mg/kg, i.p.; P<0.01). Pretreatment with clonidine failed to increase mobility when administered in combination with the 5-HT1B receptor agonist, RU 24969 (1 mg/kg, i.p.) or the 5-HT2A receptor antagonist, ketanserin (8 mg/kg, i.p.). In conclusion, clonidine-induced anti-immobility effects are more likely mediated by 5-HT1A and 5-HT2C receptors, as well as alpha-2-adrenergic autoreceptors situated on noradrenergic neurones. The results of the present study also demonstrate that serotonergic receptor function can influence alpha-2-adrenoreceptor mediated responses in the mouse forced swimming test.

Effect of the reversible monoamine oxidase-A inhibitor befloxatone on the rat 5-hydroxytryptamine neurotransmission

The aim of the present study was to assess, using in vivo electrophysiological paradigms, the effect of sustained administration of the selective and reversible monoamine oxidase-A inhibitor beflotaxone on serotonin (5-hydroxytryptamine, 5-HT) neurotransmission. In male Sprague-Dawley rats with the osmotic minipumps in place, a treatment with befloxatone (0.75 mg/kg per day, s.c.) for 2 days decreased the spontaneous firing activity of dorsal raphe 5-HT neurons. The combination of befloxatone and the 5-HT1A/1B receptor antagonist (-)-pindolol (15 mg/kg per day, s.c.) for 2 days slightly increased the firing activity of 5-HT neurons, whereas a treatment with (-)-pindolol alone for 2 days did not modify this parameter. The suppressant effects on the firing activity of 5-HT neurons of the 5-HT autoreceptor agonist lysergic acid diethylamide (LSD), injected intravenously, and of both 5-HT and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), applied by microiontophoresis, were attenuated in rats treated with befloxatone for 2 days, suggesting an early desensitization of the somatodendritic 5-HT1A receptors. The firing activity of 5-HT neurons was back to normal after a treatment for 21 days with befloxatone but the suppressant effects of LSD, 5-HT or 8-OH-DPAT was the same as in controls. In contrast, the suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of 5-HT neurons was significantly attenuated after the treatment with befloxatone for 21 days. At the postsynaptic level, the administration of the selective 5-HT1A receptor antagonist (N-[2-[4(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xanecarboxamide trihydroxychloride (WAY 100635, 100 microg/kg, i.v.) did not modify the firing activity of quisqualate-activated dorsal hippocampus CA3 pyramidal neurons in control rats. In contrast, in rats treated with befloxatone in combination with (-)-pindolol for 2 days as well as with befloxatone alone for 21 days, WAY 100635 significantly increased the firing of CA3 pyramidal neurons. In conclusion, these data suggest that when the firing activity of 5-HT neurons is normal in the presence of befloxatone, either after a two-day treatment together with (-)-pindolol or alone for 21 days, the tonic activation of postsynaptic 5-HT1A receptors is enhanced.

Mechanism of triazolo-benzodiazepine and benzodiazepine action in anxiety and depression: behavioral studies with concomitant in vivo CA1 hippocampal norepinephrine and serotonin release detection in the behaving animal

1. Real time, in vivo microvoltammetric studies were performed, using miniature carbon-based sensors, to concurrently detect norepinephrine (NE) release and serotonin (5-HT) release, in 2 separate electrochemical signals, within CA1 region of hippocampus in the freely moving and behaving, male, Sprague Dawley laboratory rat. 2. Concurrently, four parameters of open-field behavior, i.e. Ambulations, Rearing, Fine Movements and Central Ambulatory behavior (a measure of anxiety reduction behavior), were assayed by infrared photobeam detection. 3. Time course studies showed that the mechanism of action of the triazolobenzodiazepine (TBZD), adinazolam, (Deracyn) is dramatically different from that of the classical benzodiazepine (BZD), diazepam (Valium, i.e., adinazolam increased, whereas diazepam decreased, 5-HT release within CA1 region of hippocampus in the freely moving and behaving rat. 4. Adinazolam initially increased NE release and then decreased NE release in CA1 region of hippocampus in the freely moving and behaving rat whereas diazepam only decreased the electrochemical signal for NE; the decrease in NE produced by adinazolam was greater than the decrease in NE release produced by diazepam. 5. The Behavioral Activity Patterns, derived from same animal controls, simultaneously with detection of in vivo microvoltammetric signals for NE release and 5-HT release, showed that the BZD, diazepam, exhibited more potent sedative properties than did the TBZD adinazolam. 6. Hippocampal 5-HT and NE release effects of the TBZD, adinazolam, concomitant with behavioral effects lends explanation to the dual anxiolytic/antidepressant properties of the TBZDs.

Alprazolam, diazepam, yohimbine, clonidine: in vivo CA1 hippocampal norepinephrine and serotonin release profiles under chloral hydrate anesthesia

1. Although the GABA-A receptor complex has been the main focus of anti-anxiety therapy, the neural interaction in the septohippocampal circuit between GABA-A and the neurotransmitter, 5-HT, compels a study of the monoamine, 5-HT, in anxiety as well. 2. Neurochemistry for anxiety is also intimately involved with the neurotransmitter, NE. Indeed, 5-HT is a component of the dorsal ascending noradrenergic bundle and both neurotransmitters, NE and 5-HT, have been implicated in clinical depression. 3. In vivo microvoltammetric studies were performed using miniature carbon based sensors to detect NE release and concurrent 5-HT release, with 2 separate neural electrochemical signals, within CA1 region of hippocampus, in the chloral hydrate anesthetized rat. 4. Time course studies showed that both the triazolobenzodiazepine (TBZD), alprazolam, and the benzodiazepine (BZD), diazepam, decreased hippocampal NE release. 5. The in vivo and on line neurochemical profile of hippocampal 5-HT release for alprazolam differed from that of diazepam, i.e. alprazolam increased hippocampal 5-HT release, whereas diazepam decreased hippocampal 5-HT release. 6. Time course studies showed that the alpha 2-adrenergic antagonist, yohimbine, an anxiogenic agent, increased both NE and 5-HT release in CA1 region of hippocampus; the alpha 2-adrenergic agonist, clonidine, decreased NE release and increased 5-HT release in the same region. 7. Neither the profile for the TBZD, alprazolam, nor that of the BZD, diazepam, mimicked the neurochemical profile for the anxiogenic agent, yohimbine; the neurochemical profile for the TBZD, alprazolam, was similar to that of the alpha 2-adrenergic agonist, clonidine. 8. Interestingly, alprazolam's hippocampal 5-HT/NE interaction is similar to clonidine's 5-HT/NE action at alpha 2-adrenergic autoreceptors, resulting in enhanced 5-HT release. 9. Enhanced 5-HT release in hippocampus, exhibited by the atypical TBZD, alprazolam, and not by the typical BZD, diazepam, may be an underlying mechanism for the antidepressant activity exhibited by alprazolam.

Comparative behavioural profiles of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) in the murine elevated plus-maze

It has been suggested that in vivo formation of the metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) may be a major drawback in the use of buspirone as an anti-anxiety agent. To test this hypothesis, the effects of buspirone, alone or with proadifen (an inhibitor of liver microsomal enzymes) pretreatment, were contrasted with those of 1-PP in the murine elevated plus-maze test of anxiety. At 3.0 mg/kg (but not lower doses), buspirone per se had modest anxiolytic-like effects (increased percentage of open arm entries; reduced stretched-attend postures and flatback approach) that were associated with increased grooming and immobility. However, in proadifen-pretreated mice, buspirone produced behavioural depression only, with marked effects evident both at 1.0 and 3.0 mg/kg. As proadifen blocks the biotransformation of buspirone to 1-PP, these data suggest that any anxiolytic activity of buspirone in the murine plus-maze may be attributable to its principal active metabolite. Consistent with this hypothesis, 1-PP (0.5-13.5 mg/kg) produced dose-dependent anti-anxiety effects on both conventional and ethological measures that were not confounded by motoric impairment. Results are discussed in relation to biochemical and electrophysiological studies suggesting that 1-PP has a direct action at 5-HT1A receptors.

The serotonergic and noradrenergic systems of the hippocampus: their interactions and the effects of antidepressant treatments

Previous reviews have well illustrated how antidepressant treatments can differentially alter several neurotransmitter systems in various brain areas. This review focuses on the effects of distinct classes of antidepressant treatments on the serotonergic and the noradrenergic systems of the hippocampus, which is one of the brain limbic areas thought to be relevant in depression: it illustrates the complexity of action of these treatments in a single brain area. First, the basic elements (receptors, second messengers, ion channels, ...) of the serotonergic and noradrenergic systems of the hippocampus are revisited and compared. Second, the extensive interactions occurring between the serotonergic and the noradrenergic systems of the brain are described. Finally, issues concerning the short- and long-term effects of antidepressant treatments on these systems are broadly discussed. Although there are some contradictions, the bulk of data suggests that antidepressant treatments work in the hippocampus by increasing and decreasing, respectively, serotonergic and noradrenergic neurotransmission. This hypothesis is discussed in the context of the purported function of the hippocampus in the formation of memory traces and emotion-related behaviors.